Magnetoresistance effect element and magnetic memory

ABSTRACT

Provided are a magneto resistive effect element with a stable magnetization direction perpendicular to a film plane and with a controlled magnetoresistance ratio, and a magnetic memory using the magneto resistive effect element. Ferromagnetic layers  106  and  107  of the magneto resistive effect element are formed from a ferromagnetic material containing at least one type of 3d transition metal such that the magnetoresistance ratio is controlled, and the film thickness of the ferromagnetic layers is controlled on an atomic layer level such that the magnetization direction is changed from a direction in the film plane to a direction perpendicular to the film plane.

CLAIM OF PRIORITY

This application is a divisional of application Ser. No. 13/701,846,filed on Dec. 28, 2012, now pending, which claims the benefit of PCTInternational Application Number PCT/JP2011/062493, filed May 31, 2011,and Japanese Application No. JP 2010-129086, filed Jun. 4, 2010, in theJapanese Patent Office, the disclosures of which are incorporated hereinby reference.

TECHNICAL FIELD

The present invention relates to a magneto resistive effect element, anda magnetic memory provided with the magneto resistive effect element asa memory cell.

BACKGROUND

As shown in FIG. 1, a memory cell 100 of a magnetic random access memory(MRAM) has a structure such that a magneto resistive effect element 101and a select transistor 102 are electrically connected in series.Source, drain, and gate electrodes of the select transistor 102 areelectrically connected to a source line 103, a bit line 104 via themagneto resistive effect element 101, and a word line 105, respectively.The magneto resistive effect element 101 has a three-layer structure asa basic structure in which a non-magnetic layer 108 is sandwichedbetween two ferromagnetic layers, i.e., a first ferromagnetic layer 106and a second ferromagnetic layer 107. In the illustrated example, thefirst ferromagnetic layer 106 has a fixed magnetization direction andprovides a pinned layer. The second ferromagnetic layer 107 has avariable magnetization direction and provides a recording layer. Themagneto resistive effect element 101 has a low resistance when themagnetization direction of the first ferromagnetic layer 106 and themagnetization direction of the second ferromagnetic layer 107 areparallel to each other (P state), or a high resistance when thedirections are anti-parallel to each other (AP state). In the MRAM, thechanges in resistance are associated with bit information of “0” and“1”. The bit information is written by spin-torque-induced magnetizationreversal due to a current that flows through the magneto resistiveeffect element 101. When the current flows from the pinned layer to therecording layer, the magnetization of the recording layer isanti-parallel to the magnetization of the pinned layer, and the bitinformation is “1”. When the current flows from the recording layer tothe pinned layer, the magnetization of the recording layer is parallelto the magnetization of the pinned layer, and the bit information is“0”. Because the speed of magnetization reversal by the current is onthe order of one nanosecond, the MRAM is capable of writing at very highspeed. Further, because the recording of bit information is based on thedirection of magnetization of the recording layer, the MRAM isnon-volatile and can reduce power consumption during standby. Thus, theMRAM is gaining attention as a next-generation memory.

While FIG. 1 shows the case in which, in the magneto resistive effectelement 101, the first ferromagnetic layer 106 is the pinned layer andthe second ferromagnetic layer 107 is the recording layer, a similarMRAM operation can be performed when the first ferromagnetic layer 106is configured as the recording layer with a variable magnetizationdirection and the second ferromagnetic layer 107 is configured as thepinned layer with a fixed magnetization direction. In this case, too,the magnetization of the recording layer is anti-parallel to themagnetization of the pinned layer when a current flows from the pinnedlayer to the recording layer, such that the bit information is “1”. Whenthe current flows from the recording layer to the pinned layer, themagnetization of the recording layer is parallel to the magnetization ofthe pinned layer, and the bit information is “0”.

RELATED ART DOCUMENT

-   Non-patent Document 1: S. MANGIN, D. RAVELOSONA, J. A. KATINE, M. J.    CAREY, B. D. TERRIS and ERIC E. FULLERTON, “Current-induced    magnetization reversal in nanopillars with perpendicular    anisotropy”, Nature Mater., 5, 210 (2006)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

In order to realize a MRAM, several problems need to be overcome. Forexample, three characteristics of the magneto resistive effect elementas a recording element, namely the magnetoresistance ratio (MR ratio),write current density, and thermal stability factor, need to besatisfied. These conditions may vary depending on the integration level,minimum process dimensions, operating speed, and the like of the MRAM.For example, as the read speed is increased, higher magnetoresistanceratio values are required; generally, a high magnetoresistance ratio of70% to 100% is required. Further, the write current density needs to benot more than 2×10⁶ A/cm² so as to achieve an increase in write speedand a decrease in power consumption. For ensuring a record retentiontime of 10 years or more and preventing erroneous writing, the thermalstability factor of 80 or higher is required.

In a known configuration, in order to achieve a high magnetoresistanceratio, a material including a 3d transition metal element is used forthe first ferromagnetic layer and the second ferromagnetic layer, whileMgO is used for the non-magnetic layer. In this case, the materialincluding the 3d transition metal element may preferably have a bccstructure. This is because of the advantage that, when the materialincluding the 3d transition metal element has the bcc structure,coherent conduction with MgO is realized, whereby the magnetoresistanceratio can be readily increased. In this case, the magnetizationdirections of the first ferromagnetic layer and the second ferromagneticlayer are parallel to the film plane, as shown in FIG. 1. On the otherhand, it has been suggested that when a multilayer film of Co and Pt, Niand Pt, and the like, or a perpendicular magnetic anisotropy materialrepresented by alloys such as FePt and TbFeCo, is used in the firstferromagnetic layer and the second ferromagnetic layer, as described inNon-patent Document 1, low write current density and high thermalstability factor can be realized. This is due to the magnetizationdirections of the first ferromagnetic layer and the second ferromagneticlayer becoming perpendicular to the film plane. However, in the case ofthe combination of these perpendicular magnetic anisotropy materials andMgO, the magnetoresistance ratio becomes small. Thus, various methodshave been tried to increase the MR ratio. For example, a material of thebcc structure with magnetization parallel to the film plane andcontaining a 3d transition metal element is inserted between MgO and theperpendicular magnetic anisotropy material. However, in this method, thestructure is complicated and problems remain, such the control of themagnetization direction of the material including the 3d transitionmetal element and the less than expected increase in magnetoresistanceratio.

Means for Solving the Problems

According to the present invention, the material used for at least oneof a first ferromagnetic layer and a second ferromagnetic layer of amagneto resistive effect element is a material such as CoFe and CoFeBcontaining at least one type of 3d transition metal such as Co or Fe, ora Heusler alloy represented by Co₂MnSi, Co₂FeAl, Co₂CrAl, and the likeso that the magnetoresistance ratio can be controlled. Use of thesematerials enables realization of coherent tunneling conduction ofelectrons by a MgO barrier layer and the Δ1 band, whereby a high MRratio can be realized. Because Heusler alloys are a half metal materialand have high spin polarizability (approximately 100%), they areeffective in realizing an even higher MR ratio than possible withconventional ferromagnets, such as CoFe. Heusler alloys have a smalldamping factor α and are an effective material for decreasing the writecurrent density J_(c0). Normally, when a magneto resistive effectelement is formed from materials such as CoFe or CoFeB, themagnetization direction of the ferromagnetic layers is oriented in adirection parallel to the film plane. However, the present inventorshave developed a technology for realizing a low write current densityand a high thermal stability factor by making the magnetizationdirection perpendicular to the film plane by controlling the filmthickness of the ferromagnetic layers on an atomic layer level.

FIG. 2 shows the film thickness necessary for making the magnetizationdirection perpendicular to the film plane versus the temperature in anannealing step of the manufacturing process, in an example in whichCoFeB is used for the ferromagnetic layers. In the example, annealingwas conducted for an hour. The white dots in FIG. 2 indicate upperlimits of the film thickness, while the black dots indicate lowerlimits. As shown, the range of film thickness of CoFeB in which themagnetization direction becomes perpendicular to the film plane variesin accordance with the annealing temperature.

The example of FIG. 2 is for CoFeB, and the relationship between thefilm thickness necessary for the magnetization direction to beperpendicular to the film plane and the annealing temperature may differfrom FIG. 2 when the material contains at least one type of other 3dtransition metal, such as CoFe or Fe. However, the magnetizationdirection can be changed from being parallel to perpendicular withrespect to the film plane by suitably controlling the film thickness forthe material. The cause of the magnetization direction becomingperpendicular to the film plane is believed to involve a specific changein anisotropy at the interface of CoFeB and the like. By forming a thinfilm by controlling the film thickness of CoFeB on an atomic layerlevel, the ratio of volume in which the interfacial effect is presentrelative to the volume of the CoFeB layer can be increased. Thus, theeffect of specific anisotropy at the interface becomes pronounced suchthat the magnetization direction becomes perpendicular to the filmplane. The effect is particularly increased at the interface between anoxygen-containing compound represented by MgO, Al₂O₃, SiO₂, and thelike, and a ferromagnetic material containing at least one type of 3dtransition metal, such as Co and Fe, whereby the magnetization tends tobe more easily oriented in the direction perpendicular to the filmplane.

FIG. 3 shows the magnetoresistance ratio of the magneto resistive effectelement in an example in which CoFeB is used for the first ferromagneticlayer and the second ferromagnetic layer, versus the annealingtemperature, with MgO used for the non-magnetic layer. As the annealingtemperature is increased, the magnetoresistance ratio increases. Thus,in this example, annealing may be performed at approximately 250° C. toobtain a magnetoresistance ratio of 70%, or at 300° C. to obtain amagnetoresistance ratio of 100%. In this case, in order to obtain amagneto resistive effect element with the magnetization directionperpendicular to the film plane when the annealing temperature is 300°C., the film thickness of the first ferromagnetic layer and the secondferromagnetic layer may be controlled to be on the order of 1.0 nm to1.6 nm, according to FIG. 2. In this way, the magneto resistive effectelement of the present invention can achieve a magnetoresistance ratioof 70% or more which is necessary for high-speed reading.

Even when other material is used, it is possible to make the magnetoresistive effect element with a desired magnetoresistance ratio and themagnetization direction oriented in a perpendicular direction to thefilm plane by investigating the relationship between the annealingtemperature and the magnetoresistance ratio in advance. FIG. 4 shows theresistance change of the magneto resistive effect element versus amagnetic field applied in a perpendicular direction with respect to thefilm plane in an example in which CoFeB is used as the material of thefirst ferromagnetic layer and the second ferromagnetic layer and MgO isused for the non-magnetic layer. In this example, the annealingtemperature was 300° C. The experimental result shows that themagnetization directions of the recording layer and the pinned layer areoriented perpendicular to the film plane, and that the resistance of theelement is changed in accordance with the magnetization reversal of therecording layer and the pinned layer due to change in applied magneticfield. The magnetoresistance ratio at this time was 100%.

Effects of the Invention

By applying the present invention, a magneto resistive effect elementwith a large magnetoresistance ratio and a magnetization directionperpendicular to the film plane can be easily made. When it is desiredto control the magnetoresistance ratio, the annealing temperature may becontrolled and the film thickness of the first ferromagnetic layer andthe second ferromagnetic layer, which are formed with a non-magneticlayer sandwiched therebetween, may be adjusted, whereby a magnetoresistive effect element can be made in which a perpendicularmagnetization direction with respect to the film plane is maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a basic structure of a memory cell of amagnetic memory.

FIG. 2 shows changes in the film thickness necessary for themagnetization direction of a magneto resistive effect element to becomeperpendicular to the film plane, versus the temperature in an annealingstep in a case where CoFeB is used for a first ferromagnetic layer and asecond ferromagnetic layer.

FIG. 3 shows a change in the magnetoresistance ratio of the magnetoresistive effect element versus the temperature in the annealing step inthe case where CoFeB is used for the first ferromagnetic layer and thesecond ferromagnetic layer.

FIG. 4 shows a resistance change in the magneto resistive effect elementversus magnetic field application in a perpendicular direction to thefilm plane in the case where CoFeB is used for the first ferromagneticlayer and the second ferromagnetic layer.

FIG. 5 is a schematic cross sectional view of an example of the magnetoresistive effect element according to the present invention.

FIG. 6A shows a CoFeB film thickness dependency of the damping factor αof ferromagnet CoFeB.

FIG. 6B shows a CoFeB film thickness dependency of K_(eff)·t.

FIG. 7 shows the probability of magnetization reversal in a recordinglayer and a pinned layer of the magneto resistive effect elementaccording to the present invention.

FIG. 8 is a schematic cross sectional view of an example of the magnetoresistive effect element according to the present invention.

FIG. 9 is a schematic cross sectional view of an example of the magnetoresistive effect element according to the present invention.

FIG. 10 is a conceptual diagram of an example of a magnetic memoryaccording to the present invention.

MODE FOR CARRYING OUT THE INVENTION

In the following, a magnetic memory and a magneto resistive effectelement to which the present invention is applied will be described indetail with reference to the drawings.

First Embodiment

FIG. 5 schematically shows a structure of a magneto resistive effectelement according to the first embodiment. The magneto resistive effectelement 101 is provided with a first ferromagnetic layer 106 with afixed magnetization direction; a second ferromagnetic layer 107 with avariable magnetization direction; and a non-magnetic layer 108electrically connected between the first ferromagnetic layer and thesecond ferromagnetic layer. The material of the first ferromagneticlayer 106 and the second ferromagnetic layer 107 is Co₂₀Fe₆₀B₂₀, whilethe non-magnetic layer 108 is formed from MgO with a thickness of 1 nm.The first ferromagnetic layer 106 has a film thickness of 1.0 nm, andthe second ferromagnetic layer has a film thickness of 1.2 nm. For anunderlayer 503 and a capping layer 504, Ta with a thickness of 5 nm isused. A layered thin film with the configuration of FIG. 5 is made bysputtering in ultrahigh vacuum, and is thereafter annealed at 300° C.for crystallization of the first ferromagnetic layer, the secondferromagnetic layer, and the non-magnetic layer.

With reference to FIG. 2, the magnetic easy axis of the CoFeB layers ofthe first ferromagnetic layer 106 and the second ferromagnetic layer 107can be made perpendicular to the film plane by controlling the filmthickness of the layers to be on the order of 1.0 nm to 1.6 nm when theannealing temperature is 300° C. According to the present embodiment,the first ferromagnetic layer 106 has a film thickness of 1.0 nm and thesecond ferromagnetic layer 107 has a film thickness of 1.2 nm. Byapplying these film thicknesses, magnetization 501 of the firstferromagnetic layer and magnetization 502 of the second ferromagneticlayer are oriented in a perpendicular direction, as shown in FIG. 5. Byproviding the film thickness difference between the first ferromagneticlayer 106 and the second ferromagnetic layer 107, the ease ofmagnetization reversal of the pinned layer and the recording layer canbe controlled.

The relationship between the film thickness of CoFeB and the ease ofmagnetization reversal of the recording layer and the pinned layer(i.e., the difference in current density J_(c0) required formagnetization reversal) will be described in greater detail. The currentdensity J_(c0) required for magnetization reversal of the magneticlayers can be expressed by the following expression.J_(c0)∝α·K_(eff)·t  (1)

where α is the Gilbert damping factor, t is the film thickness of themagnetic layers, and K_(eff) is the perpendicular magnetic anisotropyenergy density of the magnetic layers.

The values of α and K_(eff) vary depending on the film thickness ofCo₂₀Fe₆₀B₂₀. FIGS. 6A and 6B show the Co₂₀Fe₆₀B₂₀ film thicknessdependency of α and K_(eff)·t (product of K_(eff) and t). As shown inFIGS. 6A and 6B, α and K_(eff)·t increase as the Co₂₀Fe₆₀B₂₀ filmthickness is decreased. From these characteristics and expression (1),it can be seen that the write current density J_(c0) increases as theCo₂₀Fe₆₀B₂₀ film thickness is decreased. For the above reasons, in theconfiguration of the first embodiment, magnetization reversal isdifficult to occur in the pinned layer (1.0 nm) compared with therecording layer (1.2 nm), so that the magnetization direction of thepinned layer can be stably retained when a current is caused to flow forrewriting information in the recording layer.

FIG. 7 shows the results of calculation of the probability ofmagnetization reversal of the recording layer and the pinned layer inthe element according to the present embodiment. As shown, when theapplied voltage is positive, a current flows through the magnetoresistive effect element from bottom (pinned layer 106) to top(recording layer 107). When the voltage is applied in the positivedirection and more than a certain current flows through the element, themagnetization of the recording layer 107 is reversed (change at A in thefigure). At this time, the magnetization direction of the pinned layer106 is still retained. As the positive voltage is further increased andthe current flows, the magnetization of the pinned layer 106 is alsoeventually reversed (change at B in the figure); however, the voltage(current) required for magnetization reversal of the pinned layer 106 issignificantly greater than the value required for the reversal of therecording layer 107. On the other hand, when a negative voltage isapplied, a current flows from top (recording layer 107) to bottom(pinned layer 106) of the element. In this case, too, the voltage(current) required for the magnetization reversal of the pinned layer106 (change at D in the figure) is significantly greater than the valuefor the magnetization reversal of the recording layer 107 (change at Cin the figure), as in the case of the application of positive voltage.Thus, as described above, according to the present embodiment, the easeof magnetization reversal is controlled by providing a film thicknessdifference between the recording layer and the pinned layer, whereby anoperation can be implemented in which the magnetization direction of thepinned layer can be stably retained at the time of rewriting informationof the recording layer (magnetization reversal).

Preparation and evaluation of the element with the configuration of thefirst embodiment has shown a resistance change due to magnetizationreversal in perpendicular direction and a MR ratio of 100% or higher. Ithas also been confirmed that the magnetization of the pinned layer canbe stably retained at the time of rewriting of the recording layer, inagreement with the calculation results shown in FIG. 7.

According to the present embodiment, the first ferromagnetic layer 106is used as the pinned layer while the second ferromagnetic layer 107 isused as the recording layer. However, the top-bottom positions of thelayers may be switched such that the film thickness of the ferromagneticlayer disposed over the non-magnetic layer 108 is decreased comparedwith the ferromagnetic layer disposed under the non-magnetic layer 108.In this case, the ferromagnetic layer disposed over the non-magneticlayer 108 is the pinned layer.

While according to the present embodiment CoFeB is used as the materialof the first ferromagnetic layer 106 and the second ferromagnetic layer107, other materials may be used. For example, a material containing atleast one type of 3d transition metal element, such as CoFe and Fe, isused. Further, a Heusler alloy represented by Co₂MnSi, Co₂FeAl, Co₂CrAl,and the like may be used. Heusler alloys are a half metal material andtherefore have high spin polarizability, so that the MR ratio can befurther increased. In addition, Heusler alloys have a small dampingfactor α compared with conventional ferromagnets. The materials thathave been considered as perpendicular magnetization material generallyhave a large damping factor, such as on the order of 0.1 for a Co/Ptmultilayer film. In comparison, CoFeB used in the present embodiment hasa low damping factor of not more than 0.03 (depending on filmthickness). A Heusler alloy, such as Co₂FeMnSi, has an even lowerdamping factor of less than 0.01. Thus, by applying a Heusler alloy withthe small damping factor α in the recording layer, the write currentdensity J_(c0) can be further decreased.

While according to the present embodiment MgO is used as the material ofthe non-magnetic layer 108, other materials may be used. For example, anoxygen-containing compound such as Al₂O₃ and SiO₂, a semiconductor suchas ZnO, or a metal such as Cu is used. When an amorphous insulator ofAl₂O₃, SiO₂, and the like is used as the barrier layer, the MR ratio maybe decreased compared with the case where MgO is used. However, becauseof the effect of making the magnetization of the first ferromagneticlayer 106 and the second ferromagnetic layer 107 perpendicular, thefunction as a magneto resistive effect element with perpendicularmagnetization can be provided. When a metal such as Cu is used for thenon-magnetic layer 108, an oxygen-containing compound may be used forthe underlayer 503 and the capping layer 504 so as to cause themagnetization of the first ferromagnetic layer 106 and the secondferromagnetic layer 107 to be perpendicular.

Second Embodiment

The second embodiment proposes a magneto resistive effect element inwhich layers of different crystalline structures are applied in thepinned layer and the recording layer.

The magneto resistive effect element according to the second embodimentis similar to the first embodiment shown in FIG. 5 in basic structureand the film thickness of the various layers. For the non-magnetic layer108, MgO (film thickness: 1 nm) is used, while Ta (film thickness: 5 nm)is used for the underlayer 503 and the capping layer 504. The secondembodiment differs from the first embodiment in that crystallizedCo₂₀Fe₆₀B₂₀ (film thickness: 1 nm) is used for the first ferromagneticlayer 106 as the pinned layer while Co₂₀Fe₆₀B₂₀ (film thickness: 1.2 nm)in amorphous state is used for the second ferromagnetic layer 107 as therecording layer. The magnetic anisotropy energy K_(eff) is greater incrystalline state than in amorphous state. As described with referenceto the first embodiment, the write current density J_(c0) required formagnetization reversal of the magnetic layer depends on K_(eff). Thus,in the above configuration, magnetization reversal is difficult to occurin the pinned layer compared with the recording layer. Accordingly, anoperation can be implemented in which the magnetization direction of thepinned layer can be stably retained at the time of a writing operationfor the recording layer.

A method for making a layered film for the element according to thesecond embodiment will be described with reference to FIG. 5. Theunderlayer 503, the first ferromagnetic layer 106, and the non-magneticlayer 108 are layered by sputtering at ultrahigh vacuum and roomtemperature, followed by annealing the laminated layers at 350° C. Atthis time, Co₂₀Fe₆₀B₂₀ of the first ferromagnetic layer 106 is inamorphous state at the time of film formation at room temperature but iscrystallized by the subsequent annealing. Thereafter, the temperature isbrought back to room temperature, and the second magnetic layer 107 andthe capping layer 504 are layered. By this method, the layered film witha structure such that the second ferromagnetic layer 107 is in amorphousstate and the first ferromagnetic layer 106 is crystallized can berealized. Although CoFeB is in amorphous state, the magnetizationdirection can be made perpendicular by controlling the film thickness.

Preferably, in order to obtain a higher MR ratio in the element made bythe above method, annealing is performed at temperature of approximately200° C. after the layered film is made. In this way, crystallizationproceeds only at the interface with the non-magnetic layer 108 while thesecond ferromagnetic layer 107 is generally in amorphous state, wherebyan increase in MR ratio can be achieved.

Preparation and evaluation of the element according to the secondembodiment have shown a resistance change due to magnetization reversalin perpendicular direction and a MR ratio of not less than 100%. It hasalso been confirmed that the magnetization of the pinned layer can bestably retained at the time of rewriting of the recording layer.

In another method, CoFe as crystalline material may be used for theferromagnetic layer for the pinned layer, while amorphous CoFeB may beused for the ferromagnetic layer for the recording layer.

While according to the present embodiment MgO is used as the material ofthe non-magnetic layer 108, other materials may be used. For example, anoxygen-containing compound such as Al₂O₃ and SiO₂, a semiconductor suchas ZnO, or a metal such as Cu is used. When an amorphous insulator ofAl₂O₃, SiO₂, and the like is used as the barrier layer, the MR ratio maybe decreased compared with the case where MgO is used. However, becauseof the effect of causing the magnetization of the first ferromagneticlayer 106 and the second ferromagnetic layer 107 to be perpendicular,the function as a magneto resistive effect element with perpendicularmagnetization can be provided. When a metal such as Cu is used in thenon-magnetic layer 108, an oxygen-containing compound may be used in theunderlayer 503 and the capping layer 504 so as to cause themagnetization of the first ferromagnetic layer 106 and the secondferromagnetic layer 107 to be perpendicular.

While in the foregoing embodiment a film thickness difference isprovided between the first ferromagnetic layer 106 and the secondferromagnetic layer 107, the two layers may have the same film thicknessand yet the operation as a magneto resistive effect element withperpendicular magnetization can be provided. In this case, too, becauseof the difference in crystalline structure between the firstferromagnetic layer 106 and the second ferromagnetic layer 107, there isa difference in perpendicular magnetic anisotropy between the layers.Thus, magnetization reversal is more difficult to occur in the firstferromagnetic layer 106 as the pinned layer than in the secondferromagnetic layer 107 as the recording layer. Accordingly, althoughthe magnetization stability of the pinned layer may be decreasedcompared with the configuration according to the foregoing embodiment,the magnetization direction of the pinned layer can be fixed at the timeof rewriting the recording layer.

Third Embodiment

The third embodiment proposes a magneto resistive effect element suchthat the magnetization of the pinned layer is stabilized by anon-magnetic layer adjoining the pinned layer.

The magneto resistive effect element according to the third embodimentis similar to the first embodiment shown in FIG. 5 in basic structureand the film thickness of the various layers. For the firstferromagnetic layer 106, Co₂₀Fe₆₀B₂₀ (film thickness: 1 nm) is used; forthe second ferromagnetic layer 107, Co₂₀Fe₆₀B₂₀ (film thickness: 1.2 nm)is used; and for the non-magnetic layer 108, MgO (film thickness: 1 nm)is used. The third embodiment differs from the first embodiment in thatPt (film thickness: 5 nm) is used for the underlayer 503, and Ta (filmthickness: 5 nm) is used for the capping layer 504. After the layeredfilm is made, annealing is performed at 300° C.

When a material with strong spin-orbit interaction, such as Pt as usedfor the underlayer 503 according to the third embodiment, is connectedto a magnetic layer, the damping factor α of the magnetic layerincreases. As described with reference to expression (1) in the firstembodiment, as α increases, the write current density J_(c0) isincreased. On the other hand, in the capping layer 504 connected on therecording layer side, it is preferable to use a non-magnetic materialwith weak spin-orbit interaction such that the damping factor α of theadjacent magnetic layer is decreased, such as Ta used in the presentembodiment, Cu, or Mg. By such combinations, the J_(c0) of the pinnedlayer with a large α is increased compared with the recording layer withsmall α. As a result, an erroneous operation in which the magnetizationof the pinned layer is erroneously reversed by the current that flows atthe time of rewriting information in the recording layer can beprevented, and a stable operation can be implemented.

Preparation and evaluation of the element with the configuration of thethird embodiment has shown a resistance change due to magnetizationreversal in perpendicular direction and a MR ratio of not less than100%. It has also been confirmed that the magnetization of the pinnedlayer can be stably retained at the time of rewriting the recordinglayer.

While according to the present embodiment the first ferromagnetic layer106 is used as the pinned layer and the second ferromagnetic layer 107is used as the recording layer, the top-bottom positions of the layersmay be switched such that the film thickness of the ferromagnetic layerdisposed over the non-magnetic layer 108 is decreased compared with thefilm thickness of the ferromagnetic layer disposed under the firstnon-magnetic layer 108. Thus, the ferromagnetic layer disposed over thenon-magnetic layer 108 provides the pinned layer. In this case, Pt maybe used for the non-magnetic layer (capping layer 504) adjoining theferromagnetic layer disposed over the non-magnetic layer 108, while Tamay be used for the non-magnetic layer (underlayer 503) adjoining theferromagnetic layer disposed under the non-magnetic layer 108.

While according to the present embodiment CoFeB is used as the materialof the first ferromagnetic layer 106 and the second ferromagnetic layer107, other materials may be used. For example, a material containing atleast one type of 3d transition metal element, such as CoFe or Fe, isused. Further, a Heusler alloy represented by Co₂MnSi, Co₂FeAl, Co₂CrAl,and the like may be used. Heusler alloys are a half metal material andtherefore have a high spin polarizability such that the MR ratio can befurther increased. Heusler alloys have a small damping factor α comparedwith conventional ferromagnets. The materials that have been consideredas a perpendicular magnetization material generally have a large dampingfactor, such as on the order of 0.1 for a Co/Pt multilayer film. Incomparison, CoFeB used in the present embodiment has a low dampingfactor of not more than 0.03 (depending on film thickness). A Heusleralloy, such as Co₂FeMnSi, has an even lower damping factor of less than0.01. Thus, by utilizing a Heusler alloy with the small damping factor αin the recording layer, the write current density J_(c0) can be furtherdecreased.

While according to the present embodiment Pt is used for thenon-magnetic layer 503 (underlayer) adjoining the first ferromagneticlayer 106, i.e., the pinned layer, other materials with strongspin-orbit interaction, such as Pd, may be used.

Further, while according to the present embodiment MgO is used as thematerial of the non-magnetic layer 108, other materials may be used. Forexample, an oxygen-containing compound such as Al₂O₃ and SiO₂, or asemiconductor such as ZnO, may be used. When an amorphous insulator ofAl₂O₃, SiO₂, and the like is used as the barrier layer, the MR ratio maybe decreased compared with the case where MgO is used. However, becauseof the effect of making the magnetization of the first ferromagneticlayer 106 and the second ferromagnetic layer 107 perpendicular, thefunction as a magneto resistive effect element with perpendicularmagnetization can be provided.

Further, while according to the foregoing embodiment the film thicknessdifference is provided between the first ferromagnetic layer 106 and thesecond ferromagnetic layer 107, the layers may have the same filmthickness and yet the operation as a magneto resistive effect elementwith perpendicular magnetization can be provided. In this case, too,because of the effect of the underlayer 503 and the capping layer 504,the damping factors α of the first ferromagnetic layer 106 and thesecond ferromagnetic layer 107 are varied such that magnetizationreversal is difficult to occur in the first ferromagnetic layer 106providing the pinned layer compared with the second ferromagnetic layer107 providing the recording layer. Thus, although the stability ofmagnetization of the pinned layer may be decreased compared with theforegoing embodiment, the magnetization direction of the pinned layercan be fixed at the time of rewriting of the recording layer.

Fourth Embodiment

The fourth embodiment proposes a magneto resistive effect element suchthat the magnetization of the pinned layer is stabilized by anon-magnetic layer adjoining the pinned layer, as in the thirdembodiment.

The magneto resistive effect element according to the fourth embodimentis similar to the first embodiment shown in FIG. 5 in basic structureand the film thickness of the various layers. For the firstferromagnetic layer 106, Co₂₀Fe₆₀B₂₀ (film thickness: 1 nm) is used; forthe second ferromagnetic layer 107, Co₂₀Fe₆₀B₂₀ (film thickness: 1.2 nm)is used; and for the non-magnetic layer 108, MgO (film thickness: 1 nm)is used. The fourth embodiment differs from the first embodiment in thatMgO (film thickness: 1 nm) is used for the underlayer 503, and Ta (filmthickness: 5 nm) is used for the capping layer 504. After the layeredfilm according to the fourth embodiment is made, annealing is performedat 300° C.

As described with reference to the first embodiment, the magnetizationof CoFeB of the first ferromagnetic layer 106 and the secondferromagnetic layer 107 is oriented in a perpendicular direction by achange in anisotropy at the interface between MgO of the non-magneticlayer 108 and the adjoining layers. This effect is particularlyexhibited when an oxygen-containing compound, such as MgO, is adjacent.According to the fourth embodiment, the underlayer 503 of MgO isconnected to the first ferromagnetic layer 106 as the pinned layer. Inthis way, the magnetization of the pinned layer is more stabilized inthe perpendicular direction; namely, K_(eff) of expression (1) isincreased. As a result, as will be seen from expression (1), the currentdensity J_(c0) required for magnetization reversal is increased. Becauseof this effect, the magnetization of the pinned layer is stably retainedeven when a current is caused to flow through the element for rewritinginformation in the recording layer.

Preparation and evaluation of the element according to the fourthembodiment has shown a resistance change due to magnetization reversalin perpendicular direction and a MR ratio of not less than 100%. It hasalso been confirmed that the magnetization of the pinned layer can bestably retained at the time of rewriting the recording layer.

While according to the present embodiment the first ferromagnetic layer106 is used as the pinned layer and the second ferromagnetic layer 107is used as the recording layer, the top-bottom positions of the layersmay be switched such that the film thickness of the ferromagnetic layerdisposed over the non-magnetic layer 108 is decreased compared with theferromagnetic layer disposed under the non-magnetic layer 108. In thiscase, the ferromagnetic layer disposed over the non-magnetic layer 108is the pinned layer. Further, in this case, MgO is used for thenon-magnetic layer (capping layer 504) adjoining the ferromagnetic layerdisposed over the non-magnetic layer 108, while Ta is used for thenon-magnetic layer (underlayer 503) adjoining the ferromagnetic layerdisposed under the non-magnetic layer 108.

While in the present embodiment CoFeB is used as the material of thefirst ferromagnetic layer 106 and the second ferromagnetic layer 107,other materials may be used. For example, a material containing at leastone type of 3d transition metal element, such as CoFe or Fe, is used.Further, a Heusler alloy represented by Co₂MnSi, Co₂FeAl, Co₂CrAl, andthe like may be used. Heusler alloys are a half metal material andtherefore have high spin polarizability such that the MR ratio can befurther increased. Heusler alloys have a small damping factor α comparedwith conventional ferromagnets. The materials that have been consideredas a perpendicular magnetization material generally have a high dampingfactor, such as on the order of 0.1 for a Co/Pt multilayer film. Incomparison, CoFeB used in the present embodiment has a low dampingfactor of not more than 0.03 (depending on film thickness). However, aHeusler alloy, such as Co₂FeMnSi, has an even lower damping factor ofless than 0.01. Thus, by applying a Heusler alloy with the small dampingfactor α in the recording layer, the write current density J_(c0) can befurther decreased.

While according to the present embodiment MgO is used for thenon-magnetic layer (underlayer 503) adjacent the first ferromagneticlayer 106, i.e., the pinned layer, other compounds containing oxygen,such as Al₂O₃ or SiO₂, may be used.

While according to the present embodiment MgO is used as the material ofthe non-magnetic layer 108, other materials may be used. For example, anoxygen-containing compound such as Al₂O₃ or SiO₂, or a semiconductorsuch as ZnO, is used. When an amorphous insulator of Al₂O₃, SiO₂, andthe like is used as the barrier layer, the MR ratio may be decreasedcompared with the case where MgO is used. However, because of the effectof making the magnetization of the first ferromagnetic layer 106 and thesecond ferromagnetic layer 107 perpendicular, the function as a magnetoresistive effect element with perpendicular magnetization can beprovided.

Further, while according to the present embodiment a film thicknessdifference is provided between the first ferromagnetic layer 106 and thesecond ferromagnetic layer 107, the layers may have the same filmthickness and yet the operation as a magneto resistive effect element ofperpendicular magnetization can be provided. In this case, too, becauseof the effect of the underlayer 503 and the capping layer 504, thedamping factors α of the first ferromagnetic layer 106 and the secondferromagnetic layer 107 are varied such that magnetization reversal isdifficult to occur in the first ferromagnetic layer 106 providing thepinned layer compared with the second ferromagnetic layer 107 providingthe recording layer. Thus, while the stability of the magnetization ofthe pinned layer may be decreased compared with the configuration of theforegoing embodiment, the magnetization direction of the pinned layercan be fixed at the time of rewriting the recording layer.

Fifth Embodiment

The fifth embodiment proposes an element with a structure such that amaterial of the same material type but with different composition ratiosis applied in the pinned layer and the recording layer.

The magneto resistive effect element according to the fifth embodimentis similar to the first embodiment shown in FIG. 5 in basic structureand the film thickness of the various layers. However, according to thefifth embodiment, a material with different compositions is used for therespective magnetic layers; specifically, Co₂₀Fe₆₀B₂₀ (film thickness: 1nm) is used for the first ferromagnetic layer 106 while Co₄₀Fe₄₀B₂₀(film thickness: 1.2 nm) is used for the second ferromagnetic layer 107.The perpendicular magnetic anisotropy energy density K_(eff) is higherin Co₂₀Fe₆₀B₂₀ with a higher Fe composition ratio than in Co₄₀Fe₄₀B₂₀.Because the write current density J_(c0) required for magnetizationreversal of the magnetic layer depends on K_(eff), magnetizationreversal is difficult to occur in the pinned layer compared with therecording layer according to the above configuration. Thus, themagnetization direction of the pinned layer is stably retained at thetime of a write operation for the recording layer, so that a highlyreliable operation can be implemented.

Preparation and evaluation of the element according to the fifthembodiment has shown a resistance change by magnetization reversal inperpendicular direction and a MR ratio of not less than 100%. It hasalso been confirmed that the magnetization of the pinned layer can bestably retained at the time of rewriting the recording layer.

While according to the present embodiment CoFeB is used as the materialof the first ferromagnetic layer 106 and the second ferromagnetic layer107, other materials may be used. For example, a material containing atleast one type of 3d transition metal element, such as CoFe or Fe, isused. Obviously, effects similar to those of the present embodiment canbe obtained by applying crystallized Co₄₀Fe₄₀B₂₀ for the firstferromagnetic layer 106 providing the pinned layer and Co₂₀Fe₆₀B₂₀ inamorphous state for the second ferromagnetic layer 107 providing therecording layer, as in the second embodiment.

While according to the present embodiment Ta is used for the underlayer503, in order to stabilize the magnetization of the pinned layer more,it may be effective to use a metal with large spin-orbit interaction,such as Pt or Pd, or an oxygen-containing compound, such as MgO, as inthe third embodiment or the fourth embodiment.

While according to the present embodiment MgO is used as the material ofthe non-magnetic layer 108, other materials may be used. For example, anoxygen-containing compound such as Al₂O₃ or SiO₂, or a semiconductorsuch as ZnO is used. When an amorphous insulator of Al₂O₃, SiO₂, and thelike is used as the barrier layer, the MR ratio may be decreasedcompared with the case where MgO is used; however, because of the effectof making the magnetization of the first ferromagnetic layer 106 and thesecond ferromagnetic layer 107 perpendicular, the function as a magnetoresistive effect element with perpendicular magnetization can beprovided.

Sixth Embodiment

The sixth embodiment proposes a magneto resistive effect element suchthat the magnetization of the pinned layer is more stabilized byconnecting an antiferromagnet layer to the pinned layer.

FIG. 8 schematically shows a cross section of a layered film of theelement according to the sixth embodiment. The element according to thesixth embodiment is similar to the first embodiment shown in FIG. 5 inbasic structure and the film thickness of the various layers. For thefirst ferromagnetic layer 106, Co₂₀Fe₆₀B₂₀ (film thickness: 1 nm) isused; for the second ferromagnetic layer 107, Co₂₀Fe₆₀B₂₀ (filmthickness: 1.2 nm) is used; for the non-magnetic layer 108, MgO (filmthickness: 1 nm) is used; and for the capping layer 504, Ta (filmthickness: 5 nm) is used. The sixth embodiment differs from the firstembodiment in that NiFe (film thickness: 3 nm) is used for theunderlayer 503, and an antiferromagnetic layer 1301 of MnIr (filmthickness: 8 nm) is layered on the underlayer 503. After the layeredfilm is made, annealing is performed at 300° C.

By using the antiferromagnetic layer 1301 as an underlayer for the firstferromagnetic layer 106 providing the pinned layer, the magnetization ofthe pinned layer can be more stabilized. Thus, the erroneous operationin which the magnetization of the pinned layer is reversed by currentthat flows at the time of writing information in the recording layer canbe suppressed.

Preparation and evaluation of the element according to the sixthembodiment has shown a resistance change by magnetization reversal inperpendicular direction and a MR ratio of not less than 100%. It hasalso been confirmed that the magnetization of the pinned layer can bestably retained at the time of rewriting the recording layer.

While according to the present embodiment CoFeB is used as the materialof the first ferromagnetic layer 106 and the second ferromagnetic layer107, other materials may be used. For example, a material containing atleast one type of 3d transition metal element, such as CoFe or Fe, maybe used. Further, amorphous CoFeB may be used for the secondferromagnetic layer 107 forming the recording layer, as in the secondembodiment. A Heusler alloy represented by Co₂MnSi, Co₂FeAl, Co₂CrAl, orthe like may also be used. Heusler alloys are a half metal material andtherefore have high spin polarizability such that the MR ratio can befurther increased. Heusler alloys have small damping factor α comparedwith conventional ferromagnets. The materials that have been consideredas a perpendicular magnetization material generally have a large dampingfactor, such as on the order of 0.1 for a Co/Pt multilayer film. Incomparison, CoFeB used in the present embodiment has a low dampingfactor of not more than 0.03 (depending on film thickness). A Heusleralloy, such as Co₂FeMnSi, has an even lower damping factor of less than0.01. Thus, by applying a Heusler alloy with the small damping factor αin the recording layer, the write current density J_(c0) can be furtherdecreased.

While in the present embodiment MgO is used as the material of thenon-magnetic layer 108, other materials may be used. For example, anoxygen-containing compound such as Al₂O₃ or SiO₂, or a semiconductorsuch as ZnO, is used. When an amorphous insulator of Al₂O₃ or SiO₂ isused as the barrier layer, the MR ratio may be decreased compared withthe case where MgO is used; however, because of the effect of making themagnetization of the first ferromagnetic layer 106 and the secondferromagnetic layer 107 perpendicular, the function as a magnetoresistive effect element with perpendicular magnetization can beprovided.

Seventh Embodiment

The seventh embodiment proposes a magneto resistive effect element inwhich the magnetization of the pinned layer is more stabilized byapplying a pinned layer with a structure such that ferromagnetic layersand non-magnetic layers are alternately layered.

FIG. 9 schematically shows a cross section of a layered film of theelement according to the seventh embodiment. In the seventh embodiment,a pinned layer 1001 has a layered structure of non-magnetic layer1005/ferromagnetic layer 1004/non-magnetic layer 1003/ferromagneticlayer 1002. For the non-magnetic layer 1003 and the non-magnetic layer1005, MgO (film thickness: 0.4 nm) is used. For the ferromagnetic layer1002 and the ferromagnetic layer 1004, Co₂₀Fe₆₀B₂₀ (film thickness: 1nm) is used. By adopting this layered structure, the number ofinterfaces between ferromagnetic layers and non-magnetic layers isincreased, so that the interfacial effect for causing the magnetizationdirection of the pinned layer 1001 to be perpendicular is increased.Further, the total volume of the ferromagnetic layer portion of thepinned layer 1001 is increased, so that the magnetization direction ismore stabilized in the perpendicular direction with respect to the filmplane. As a result, the erroneous operation in which the magnetizationof the pinned layer is reversed by the current that flows at the time ofwriting of information in the recording layer can be more suppressed.According to the seventh embodiment, MgO (film thickness: 1 nm) is usedfor the non-magnetic layer 108; Ta (film thickness: 5 nm) is used forthe underlayer 503 and the capping layer 504; and Co₂₀Fe₆₀B₂₀ (filmthickness: 1.2 nm) is used for the ferromagnetic layer 107 providing therecording layer.

Preparation and evaluation of the element according to the seventhembodiment has shown a resistance change by magnetization reversal inperpendicular direction and a MR ratio of not less than 100%. It hasalso been confirmed that the magnetization of the pinned layer can bestably retained at the time of rewriting the recording layer.

In order to stabilize the magnetization of the pinned layer, the numberof the layers in the layered structure of the pinned layer may beincreased. While according to the present embodiment MgO is used for thenon-magnetic layer 1003 inserted between the ferromagnetic layer 1002and the ferromagnetic layer 1004 of the pinned layer 1001, othermaterials may be used. For example, a material containing oxygen, suchas Al₂O₃ or SiO₂, is used. Further, a metal such as Ru, Rh, V, Ir, Os,or Re may be used. In this case, due to the exchange coupling betweenthe magnetizations of the ferromagnetic layer 1002 and the ferromagneticlayer 1004, the magnetization directions of the ferromagnetic layer 1002and the ferromagnetic layer 1004 can be easily changed to parallel oranti-parallel by controlling the film thickness of the non-magneticlayer 1003.

Further, while according to the present embodiment CoFeB is used for themultiple ferromagnetic layers of the layered-structure pinned layer andthe second ferromagnetic layer 107, other materials may be used. Forexample, a material containing at least one type of 3d transition metalelement, such as CoFe or Fe, may be used. Further, a Heusler alloyrepresented by Co₂MnSi, Co₂FeAl, Co₂CrAl, or the like may be used.Heusler alloys are a half metal material and therefore have high spinpolarizability such that the MR ratio can be further increased. Heusleralloys have small damping factor α compared with conventionalferromagnets. The materials that have been considered as a perpendicularmagnetization material generally have a large damping factor, such as onthe order of 0.1 for a Co/Pt multilayer film. In comparison, CoFeB usedin the present embodiment has a low damping factor of not more than 0.03(depending on film thickness). However, a Heusler alloy, such asCo₂FeMnSi, has an even lower damping factor of less than 0.01. Thus, byapplying a Heusler alloy with the small damping factor α in therecording layer, the write current density J_(c0) can be furtherdecreased.

While according to the present embodiment MgO is used as the material ofthe non-magnetic layer 108, other materials may be used. For example, anoxygen-containing compound such as Al₂O₃ or SiO₂, or a semiconductorsuch as ZnO is used. When an amorphous insulator of Al₂O₃ or SiO₂ isused as the barrier layer, the MR ratio may be decreased compared withthe case where MgO is used; however, because of the effect of causingthe magnetization of the first ferromagnetic layer 106 and the secondferromagnetic layer 107 to be perpendicular, the function as a magnetoresistive effect element with perpendicular magnetization can beprovided.

Eighth Embodiment

According to another aspect of the present invention, a MRAM can berealized by adopting the magneto resistive effect element according tothe first through the seventh embodiments as a recording element.

As shown in FIG. 10, the MRAM according to the present invention isprovided with a plurality of bit lines 104 disposed in parallel witheach other; a plurality of source lines 103 disposed in parallel withthe bit lines 104 and with each other; and a plurality of word lines 105disposed perpendicular to the bit lines 104 and parallel with eachother. At points of intersection of the bit lines 104 and the word lines105, the memory cells 100 are disposed. The memory cells 100 areprovided with the magneto resistive effect elements 101 according to thefirst through the seventh embodiments, and the select transistors 102.The multiple memory cells 100 constitute a memory array 1401. The bitlines 104 are electrically connected to drain electrodes of the selecttransistors 102 via the magneto resistive effect elements 101. Thesource lines 103 are electrically connected to source electrodes of theselect transistors 102 via a wiring layer. The word lines 105 areelectrically connected to gate electrodes of the select transistors 102.One end of the source lines 103 and the bit lines 104 is electricallyconnected to write drivers 1402 for applying voltage and to senseamplifiers 1403. One end of the word lines 105 is electrically connectedto a word driver 1404.

In an operation for writing “0”, a voltage is applied from the writedriver 1402 to the bit line 104 while a voltage is applied from the worddriver 1404 to the word line 105 so as to cause a current to flowthrough the source line 103 via the magneto resistive effect element 101selected by the bit line 104. At this time, when the magneto resistiveeffect element 101 is configured such that, as shown in FIG. 5, thefirst ferromagnetic layer 106 is the pinned layer and the secondferromagnetic layer 107 is the recording layer, the magneto resistiveeffect element 101 has a low resistance and retains information “0”. Onthe other hand, in an operation for writing “1”, a voltage is appliedfrom the write driver 1402 to the source line 103 and a voltage isapplied from the word driver 1404 to the word line 105 so as to cause acurrent to flow through the bit line 104 via the magneto resistiveeffect element 101 selected by the source line 103. At this time, themagneto resistive effect element 101 has a high resistance and retainsinformation “1”. At the time of reading, the difference in a signal dueto resistance change is read by the sense amplifiers 1403. By adoptingthe memory array of such configuration, the MRAM can operate as anon-volatile memory in which the magnetoresistance ratio is increased,the write current density is decreased, and the thermal stability factoris increased.

DESCRIPTION OF REFERENCE SIGNS

-   100 Memory cell of magnetic memory-   101 Magneto resistive effect element-   102 Select transistor-   103 Source line-   104 Bit line-   105 Word line-   106 First ferromagnetic layer-   107 Second ferromagnetic layer-   108 Non-magnetic layer-   501 Magnetization-   502 Magnetization-   503 Underlayer-   504 Capping layer-   1001 Pinned layer-   1002 Ferromagnetic layer-   1003 Non-magnetic layer-   1004 Ferromagnetic layer-   1005 Non-magnetic layer-   1301 Antiferromagnetic layer-   1401 Memory array-   1402 Write driver-   1403 Sense amplifier-   1404 Word driver

The invention claimed is:
 1. A magnetoresistive element comprising: afirst non-magnetic layer containing oxygen; a ferromagnetic layer havinga bcc structure and containing Fe and B, disposed over the firstnon-magnetic layer, with an interfacial perpendicular magneticanisotropy at an interface therebetween that results in a magnetizationdirection of the ferromagnetic layer oriented perpendicularly to thefilm plane so that the magnetoresistive element has a magnetoresistanceratio (MR) equal to or greater than 70%; and a second non-magnetic layerdisposed over the ferromagnetic layer, the second non-magnetic layercontaining a material with a spin-orbit interaction smaller than that ofPt.
 2. The magnetoresistive element according to claim 1, the secondnon-magnetic layer contains any one of Ta, Cu and Mg.
 3. Themagnetoresistive element according to claim 1, wherein the firstnon-magnetic layer contains MgO.
 4. The magnetoresistive elementaccording to claim 1, wherein the ferromagnetic layer contains Co. 5.The magnetoresistive element according to claim 1, wherein themagnetization direction of the ferromagnetic layer is perpendicular tothe film plane resulting from a layer thickness of the ferromagneticlayer being smaller than a predetermined thickness.
 6. Themagnetoresistive element according to claim 1, wherein the MR ratio ofthe magnetoresistive element is equal to or greater than 100%.
 7. Themagnetoresistive element according to claim 1, wherein the secondnon-magnetic layer consists essentially of an oxide-free material.
 8. Amethod for producing a magnetoresistive element, comprising: forming afirst non-magnetic layer containing oxygen; forming a ferromagneticlayer having a bcc structure and containing Fe and B, over the firstnon-magnetic layer with an interfacial perpendicular magnetic anisotropyat an interface therebetween that results in a magnetization directionof the ferromagnetic layer oriented perpendicularly to the film plane sothat the magnetoresistive element has a magnetoresistance ratio (MR)equal to or greater than 70%; and forming a second non-magnetic layerover the ferromagnetic layer, the second non-magnetic layer containing amaterial with a spin-orbit interaction smaller than that of Pt.
 9. Themethod for producing a magnetoresistive element according to claim 8,wherein the second non-magnetic layer contains any one of Ta, Cu and Mg.10. The method for producing a magnetoresistive element according toclaim 8, wherein the first non-magnetic layer contains MgO.
 11. Themethod for producing a magnetoresistive element according to claim 8,wherein the ferromagnetic layer contains Co.
 12. The method forproducing a magnetoresistive element according to claim 8, wherein saidforming a ferromagnetic layer includes causing the magnetizationdirection of the ferromagnetic layer to be perpendicular to the filmplane by controlling a layer thickness of the ferromagnetic layer to besmaller than a predetermined thickness.
 13. The method for producing amagnetoresistive element according to claim 8, wherein the secondnon-magnetic layer contains any one of Ta, Cu and Mg.
 14. The method forproducing a magnetoresistive element according to claim 8, wherein thefirst non-magnetic layer contains MgO.
 15. The method for producing amagnetoresistive element according to claim 8, wherein the ferromagneticlayer contains Co.